The invention relates to a method for optimizing the emission of pollutants from a combustion system, especially an internal combustion engine.
German Patent Document DE 42 15 942 A1 teaches a device for monitoring the concentration of a plurality of pollutants contained in the exhaust from an internal combustion engine. The concentrations of oxides of nitrogen and hydrocarbons in the exhaust are adjusted to a given ratio at which a NOx reduction catalyst provided in the exhaust line operates with maximum efficiency. However, a disadvantage of this method is the fact that the emission of pollutants from the engine is not directly minimized; rather, better operating conditions for a catalyst located downstream are produced, so as to control emissions indirectly.
Particularly in internal combustion engines, many methods are known for regulating exhaust composition. Individual operating parameters that influence the exhaust composition are controlled or regulated as a function of the operating state or the percentage of an individual pollutant component in the exhaust. However changing an operating parameter generally influences not only one of the pollutant components but several of them, and inverse proportionalities often exist. Therefore, in the individual regulating or control methods, frequently the reduction of one pollutant component results in an increase in another pollutant component.
The goal of the present invention therefore is to provide a simple method for optimizing the emission from an internal combustion system, of pollutants that contain a plurality of pollutant components.
This goal is achieved by the emission control method according to the invention, in which a weighted composite signal is determined based on the measured amounts of detected pollutants, and this signal is then minimized by adjusting at least one operating parameter that influences exhaust composition.
The method according to the invention has the advantage that only one regulating input signal which more or less directly represents the quality of the exhaust is used to adjust the operating parameters that influence exhaust composition. If a plurality of such operating parameters must be adjusted, this is possible in a single common regulating process.
Since the definition of exhaust quality criteria is not a fixed value, but depends on legal guidelines or influences of society, it can thus can vary both regionally and with time. Another important advantage of the method, according to the invention, therefore, is that determination of the total signal can be adjusted in a simple manner to accommodate varying conditions. When a weighted summation of the individual pollutant components is used, for example, this can be done simply by varying the values of the weighting factors.
Using starting characteristic maps for the operating parameters can accelerate the regulating process. Moreover, if self-learning characteristic maps are used, the influence of parameters that change slowly, for example as a result of the aging process, can be eliminated.
The invention is described below for a method with two adjustable operating parameters, with reference to a drawing that shows a family of curves that represent exhaust quality as a function of the operating parameters to be adjusted. It is of course apparent that the method according to the invention can be readily adapted to accommodate other systems having more than two such parameters, and other families of operating characteristics.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.